I did some research in ATW and found something else very strange.
As I'm Dutch my default setting in ATW is 'Dutch/English pages'. One of my sites is basically in English with 1 Dutch page and a relevant page shows up at #3 so that seems fine.
When I switch to 'Any language' the index page of the same site shows up at #1.
A closer look reveals that the index page is not included in the Dutch/English search. This is odd because the index page and the Dutch page are the only ones with a language tag. All other pages are included in both searchers, I only miss www.domain.com/ and www.domain.com/index.htm.
Is this a bug in ATW? What should I do? I find it a bit tricky to simply remove the language tag and see what happens.
The first thing coming to mind is obviously the question if your language tags on those two pages are correct.
Assuming they are there are two options: Either this indeed a problem with ATW not correctly identifying those language tags, or it's that old problem with missing index pages in a slightly new variant.
I would in any case contact them through the ATW help and contact pages.